This application claims priority to German Patent Application No. 10154737.4 filed Nov. 9, 2001, which application is herein expressly incorporated by reference.
The invention relates to a device for measuring torque and direction of rotation in a drive assembly.
In order to measure torque at a rotating component, for instance at a torque-loaded driveshaft in a drive, the component is preferably provided with strain gauges. The generated electric signals are transmitted to the outside by slip ring transmitters. It is possible, in such devices, to generate high-precision torque signals which are required for laboratory measuring devices. Also, signal transmission can be effected in a contact-free way, by senders and receivers. The bridges for the strain gauges, calibrating the same and providing the electrical connections generate high costs. A significant cost factor is in the transmission of signals from the rotating shaft to the stationary components. Due to the high degree of integration of the electronic components in drives, transmission of signals suffers from a high inherent error rate. For many devices and machines, such a high degree of accuracy in this type of measuring device is not required. However, the above-mentioned devices cannot be redefined to such an extent that adequate cost levels are achieved. This is the reason why, in spite of the high degree of benefit of torque measurements for operational processes, such devices are practically never used in the drive systems of agricultural machinery. One example for integrating such a device in a drive is described in DE 42 31 412 C1.
U.S. Pat. No. 4,488,443 shows a device that measures torque at a shaft with a first transmitter disc and a second transmitter disc. The first transmitter disc is connected, in a rotationally fast way, to the shaft. The second transmitter disc is connected, in a rotationally fast way, to a tube which is co-axially arranged relative to the shaft. The tube, at a first longitudinal end that is arranged at a distance from the first transmitter disc, is connected to the shaft in a rotationally fast way. The second end of the tube is slidingly supported on the shaft. The second end of the tube is arranged to adjoin the first transmitter disc. The second transmitter disc is secured to the second end of the tube. The first transmitter disc and the second transmitter disc each have teeth, which start from an end face, that project towards the respective other transmitter disc. The teeth of the first transmitter disc and the second transmitter disc are alternatingly distributed across the circumference and are arranged at a distance from one another. A sensor is stationarily fixed relative to the shaft. The sensor records the passage of the teeth when the shaft rotates. If the torque load is high, the shaft becomes twisted so that the first transmitter disc is rotated relative to the second transmitter disc. The distances changes between the teeth of the first transmitter disc and the teeth of the second transmitter disc. The distances between the teeth as recorded by the sensor enables conclusions regarding the applied torque. However, the disadvantage is that it is not possible to determine the direction of rotation of the shaft nor the direction of the torque.
It is the object of the invention to provide a device which is suitable to determine torque and the direction of rotation of the drive assembly.
In accordance with the invention, a device to measure torque and the direction of rotation in a drive assembly has a torsion element that can be torque-loaded and rotatingly driven to transmit torque around an axis of rotation. The torsion element is in the form of a torsion shaft with a first shaft end and a second shaft end. A first transmitter element, which is journal-shaped is attached in a rotationally fast way to the torsion element transversely to the axis of rotation. When the torsion element rotates, the first transmitter element is moved on a first rotational circle. A reference element, in the form of a tube with a first tube end and a second tube end, is co-axially arranged around the torsion element. The first tube end is firmly connected to the first shaft end. A second transmitter element forms part of the reference element. The second transmittal element is arranged at the outer circumference of the second tube end of the reference element. The second transmitter element is at a reference distance from the first transmitter element. The second transmitter element is connected in a rotationally fast way to the torsion element. When the torsion element rotates, the second transmitter element is moved on a second rotational circle. The first rotational circle is located on the second rotational circle. A sensor unit is fixed and arranged at a distance from the axis of rotation. The sensor senses the passage of the transmitter element, of a reference edge or of a reference surface and generates a corresponding sequence of signals. The transmitter elements generate signals of different lengths. Also, the transmitter elements in the relevant measuring range, generate signal pauses of different lengths between the signals. An evaluation unit receives the signals. The evaluation unit determines the applied torque and the direction of rotation, from the time interval and the sequence in terms of time of the signals and signal pauses of different lengths. The second tube end of the reference element has a recess which enables the passage of the first transmitter element attached to the torsion element. Both transmitter elements are circumferentially offset in one plane on their common rotational circles. A first recess is provided at the second tube end of the reference element. A second recess is provided diametrically to the first recess. The first transmitter element, via a first projection, extends radially into the first recess and, via a second projection, the first transmitter element projects radially out of the second recess. The projecting portion of first transmitter element serves as a transmitter portion. If a predetermined maximum torque is exceeded, the reference element participates in the transmission of torque.
The degree of twisting of the torsion element varies as a function of the applied torque. As a result, the first transmitter element is rotated relative to the second transmitter element. Thus, as a function of the prevailing torque, signal intervals of different lengths occur between the signals. The length of the signal intervals enables conclusions regarding the angle of torsion and the applied torque.
Also, conclusions can be drawn regarding the direction of rotation of the torsion element. Since the transmitter elements are designed so that they generate signals of different lengths and, in the relevant measuring range, signal intervals of different lengths between the signals. For example, the first transmitter element can be longer in the circumferential direction than the second transmitter element. Further, if viewed in the circumferential direction, the distance between the first transmitter element and the second transmitter element can be smaller than the distance between the second transmitter element and the first transmitter element. Therefore, in the case of a rotation in a first direction, the long signal of the first transmitter element can be followed by a long signal interval. In such a case, in the other direction of rotation, the long signal interval would be followed by a long signal. The sequence enables the direction of rotation to be determined. Once the direction of rotation has been determined, it is also possible to determine the direction of torque.
Because the second transmitter element forms part of a reference element and because the first rotational circle is located on the second rotational circle, the passage of the transmitter elements of a reference edge or of a reference surface of the transmitter elements can be identified by only one sensor.
The second transmitter element can be provided in the form of a journal element. The second transmitter element is arranged on the outer face of the reference element and is circumferentially offset relative to the second recess from which the second projection emerges.
The journal element, that serves as the second transmitter element, is longer in the circumferential direction than the second projection which serves as the first transmitter element.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.